Lash adjuster and method of making same

ABSTRACT

A method of manufacturing a lash adjuster body for use in a lash adjuster assembly can include forming a lash adjuster body to an as-formed condition including an outer cylindrical surface and an inner cylindrical surface. The inner cylindrical surface can have a leak down portion and a blind bore. The method can also include imparting a wear resistant surface layer to at least the leak down portion of the inner cylindrical surface with a sub-critical temperature process. The method can also include preserving the leak down portion in the as-formed condition during imparting of the wear resistant surface layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2014/057760 filed Sep. 26, 2014, which claims the benefit of U.S.Patent Application No. 61/883,625 filed on Sep. 27, 2013 and U.S. PatentApplication No. 62/056,049 filed on Sep. 26, 2014. The disclosures ofthe above applications are incorporated herein by reference.

FIELD

The present disclosure is directed to a hydraulic or mechanical lashadjuster and a method of manufacturing the same.

BACKGROUND

Hydraulic or mechanical lash adjusters for internal combustion engineshave been in use for many years to eliminate clearance or lash betweenengine valve train components under varying operating conditions. Lashadjusters can maintain efficiency and reduce noise and wear in the valvetrain. In some examples, hydraulic lash adjusters can support thetransfer of energy from the valve-actuating cam to the valves throughhydraulic fluid trapped in a pressure chamber under the plunger.

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named Inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

SUMMARY

A method of manufacturing a lash adjuster body for use in a lashadjuster assembly can include forming a lash adjuster body to anas-formed condition including an outer cylindrical surface and an innercylindrical surface. The inner cylindrical surface can have a leak downportion and a blind bore. The method can also include imparting a wearresistant surface layer to at least the leak down portion of the innercylindrical surface with a sub-critical temperature process. The methodcan also include preserving the leak down portion in the as-formedcondition during imparting of the wear resistant surface layer.

According to additional features, forming can be further defined asforming a lash adjuster body with one of cold forming, stamping,drawing, metal injection molding, powdered metal sintering, andmachining. Forming can be further defined as cold-forming the lashadjuster body to the as-formed condition having functional geometry. Thepreserving can then be further defined as preserving the functionalgeometry of the leak down portion in the as-formed condition duringimparting of the wear resistant surface layer. The preserving can befurther defined as preserving the functional geometry of the leak downportion in the as-formed condition after imparting of the wear resistantsurface layer.

According to other features, imparting can be further defined asimparting a wear resistant surface layer to at least the leak downportion of the inner cylindrical surface with a sub-critical temperatureprocess selected from one of ferritic nitrocarburizing, physical vapordeposition, and chemical vapor deposition. The method can also includemaintaining a hardness of the lash adjuster body below the wearresistant surface layer after forming and during imparting. Preservingcan further comprise preserving the leak down portion of the innercylindrical surface in the as-formed condition after imparting of thewear resistant surface layer. Preserving can further comprise preservinga majority of the inner cylindrical surface in the as-formed conditionafter imparting of the wear resistant surface layer. Preserving canfurther comprise preserving a majority of the outer cylindrical surfacein the as-formed condition after imparting of the wear resistant surfacelayer. Preserving can further comprise preserving a majority of both ofthe outer cylindrical surface and the inner cylindrical surface in theas-formed condition after imparting of the wear resistant surface layer.

In other features, the method can also include annealing the lashadjuster body before imparting to relieve stresses arising duringforming. The method can also include cleaning the lash adjuster bodyafter imparting and polishing the lash adjuster body after imparting.

A lash adjuster body for use in a lash adjuster assembly can include anouter cylindrical surface and an inner cylindrical surface. The innercylindrical surface can have a leak down portion and a blind bore. Atleast the leak down portion of the inner cylindrical surface can includea wear resistant surface layer imparted with a sub-critical temperatureprocess. The leak down portion can be preserved in an as-formedcondition existing prior to the imparting of the wear resistant surfacelayer.

According to additional features, the majority of the at least one ofthe outer cylindrical surface and the inner cylindrical surface can bemodified through the sub-critical temperature process being one offerritic nitrocarburizing, physical vapor deposition, and chemical vapordeposition. The inner cylindrical surface can further comprise a plungershelf and a notch. The notch can be positioned between the leak downportion and the plunger shelf.

A lash adjuster assembly can include a lash adjuster body and a leakdown plunger. The lash adjuster body can include an outer cylindricalsurface and an inner cylindrical surface. The inner cylindrical surfacecan include a leak down portion and a blind bore. At least the leak downportion of the inner cylindrical surface can include a wear resistantsurface layer imparted with a sub-critical temperature process. The leakdown portion can be preserved in an as-formed condition existing priorto the imparting of the wear resistant surface layer. The leak downplunger can be slidably received in the inner cylindrical surfaceagainst the leak down portion.

According to additional features, a majority of the outer cylindricalsurface and a majority of the inner cylindrical surface include the wearresistant surface layer. The majorities of the outer and innercylindrical surfaces can be preserved in the as-formed conditionexisting prior to the imparting of the wear resistant surface layer. Amajority of the inner cylindrical surface can include the wear resistantsurface layer and a functional geometry of the majority of the innercylindrical surface can be maintained in the as-formed conditionexisting prior to the imparting of the wear resistant surface layer. Thewear resistant surface layer can have a depth of less than fortymicrons.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is flow chart of a process in accordance with an example of thepresent disclosure;

FIG. 2 is a cross-sectional view of a normally open lash adjusterconstructed in accordance with another example of the presentdisclosure;

FIG. 3 is a cross-sectional view of a normally closed lash adjusterconstructed in accordance with another example of the presentdisclosure;

FIG. 4 is a cross-sectional view of a normally closed lash adjusterconstructed in accordance with another example of the presentdisclosure; and

FIG. 5 is a variant cross-sectional view of a normally closed lashadjuster constructed in accordance with another example of the presentdisclosure.

DETAILED DESCRIPTION

A plurality of different embodiments of the present disclosure is shownin the Figures of the application. Similar features are shown in thevarious embodiments of the present disclosure. Similar features havebeen numbered with a common reference numeral and have beendifferentiated by an alphabetic suffix. Similar features acrossdifferent embodiments have been numbered with a common reference numeraland have been differentiated by an alphabetic suffix. Also, to enhanceconsistency, the structures in any particular drawing share the samealphabetic suffix even if a particular feature is shown in less than allembodiments. Similar features are structured similarly, operatesimilarly, and/or have the same function unless otherwise indicated bythe drawings or this specification. Furthermore, particular features ofone embodiment can replace corresponding features in another embodimentor can supplement other embodiments unless otherwise indicated by thedrawings or this specification.

With reference now to FIG. 1, a method of manufacturing a lash adjusterbody for use in a lash adjuster assembly can start at 100. At 102, alash adjuster body can be formed to an as-formed condition. Theas-formed condition can be defined as the lash adjuster body havingfunctional geometry at the completion of 102. Functional geometry refersto the fact the lash adjuster body can be operable to perform upon beingformed without further processing that would alter the geometry of thelash adjuster body.

An exemplary lash adjuster body is referenced at 20 in FIG. 2. The lashadjuster body 20 can be formed using established metal forming and/ormachining techniques with or without thermal input. Such technique couldinclude cold-forming or cold-forging or cold-heading, deep-drawing coldformed in one or more embodiments of the present disclosure. Coldforming can be a relatively high-speed manufacturing process wherebymetal is shaped at relatively lower temperatures. A cold-formedworkpiece is not necessarily heated, but can increase in temperatureduring the cold forming process. Cold forming can be carried out withoutremoving material from a workpiece. Metal can be forced beyond theelastic yield limit but below tensile strength. As used herein, the term“cold-forming” and its derivatives, are intended to encompass what isknown in the art as “cold-forging”, “cold heading” and “deep drawing”.The lash adjuster body blank can be precision cold formed, whereinworkpiece dimensions can be held to within microns. In some otherembodiments, the lash adjuster body blank can be formed with stamping,drawing, metal injection molding, powdered metal sintering, ormachining.

With reference now to FIG. 2, the lash adjuster body 20 can have anouter cylindrical surface 32 and an inner cylindrical surface 33. Theinner cylindrical surface 33 can include a leak down portion 34 and ablind bore 40. The lash adjuster body 20 can be manufactured such that amajority of at least one of the outer cylindrical surface 32 and theinner cylindrical surface 33 is maintained in an as-formed condition. Anunground condition can define one example of an as-formed condition. Forexample only, neither of the surfaces 32, 34 may be subjected togrinding in one or more embodiments of the present disclosure.Generally, grinding and machining are distinct subsets of metal removalgenerally. Grinding is a microscopic cutting operation and machining isa macroscopic cutting operation. Alternatively, at least one of thesurfaces 32, 34 is not subjected to grinding in one or more embodimentsof the present disclosure. Generally, if it is desired to grind theinner cylindrical surface 33, the outer cylindrical surface 32 must beground as well since the lash adjuster body 20 will be held by the outercylindrical surface 32 during grinding of the inner cylindrical surface33. The exemplary lash adjuster body 20 of the present disclosure isthus not over-processed.

Referring again to FIG. 1, the lash adjuster body can be annealed at 104in one or more embodiments of the present disclosure to reduce residualstresses. Processes for relieving stress alternative to annealing can beapplied in some embodiments of the present disclosure. At 106, materialcan be machined from the lash adjuster body. A lash adjuster body can bemachined by defining an aperture or by turning a groove in the outercylindrical surface of the lash adjuster body, and by metal removal toqualify over-all length. As used herein, the term “machining” can meanthe use of a chucking machine, drilling machine, turning machine, orbroaching machine to remove material.

At 108, a wear resistant surface layer can be imparted to at least aportion of the lash adjuster body. The wear resistance of the portion ofthe lash adjuster body can be enhanced by 108. The wear resistantsurface layer can be imparted to the outer cylindrical surface 32 andthe inner cylindrical surface 33 in one or more embodiments of thepresent disclosure. Alternatively, the outer cylindrical surface 32 mayor may not be imparted with a wear resistant surface layer. Anysub-critical temperature process can be applied to impart the wearresistant surface layer, such as by way of example and not limited toferritic nitrocarburizing (hereafter “FNC”), physical vapor deposition(hereafter “PVD”), or chemical vapor deposition (hereafter “CVD”). Othersub-critical temperature process can be applied as well. FNC is athermochemical surface hardening process that includes diffusion ofnitrogen and carbon onto the lash adjuster body. PVD is a process inwhich a solid coating material is evaporated by heat or by bombardmentwith ions on a workpiece to be coated. CVD is a process in which aworkpiece is exposed to one or more volatile precursors which reactand/or decompose on the workpiece to produce the desired coating. Suchprocesses for imparting a wear resistant surface layer may be employedwith or without a vacuum process to minimize or eliminate distortion.

It is noted that the order of 106 and 108 can be reversed in someembodiments of the present disclosure. In such an embodiment, themachining can include producing a side hole on the body, such asaperture 42. Alternatively, the machining could include creating anouter diameter groove such as groove 27. Alternatively, the machiningcould include creating the geometry for a hook portion such as hookportion 98 b shown in FIG. 4. The machining operation could remove aportion of the wear resistant surface layer that was previously impartedto the lash adjuster body 20. Machining can also include materialremoval to correct the overall length of the lash adjuster body 20 andinclude lead-in angles or chamfers and/or radii on the inner and outercylindrical surfaces.

According to prior art methods, the lash adjuster body would undergo aheat treatment process such as carbonitriding. Carbonitriding is ametallurgical surface modification technique that is used to increasesurface hardness of a metal. Heat-treating the lash adjuster body with aprocess such as carbonitriding can cause the geometry of the lashadjuster body to be distorted. In such scenarios, a subsequent machiningor grinding or material working step is necessary to return the lashadjuster body to its “pre-heat treated” shape or to an otherwise desiredresultant shape. In the embodiments of the present disclosure, aconventional heat treatment step is replaced by incorporating asubcritical temperature process such as FNC or PVD or CVD that imparts awear resistant surface layer and helps preserve the functional geometryof the lash adjuster body requiring no additional operations to correctdistortion. Similar to increasing hardness as provided bycarbonitriding, FNC enhances the wear resistance of a surface. In thisregard, substantial time and cost savings may be realized bymanufacturing the lash adjuster body according to the present method.

The functional geometry of the lash adjuster body is preserved as thewear resistant surface is being imparted. The lash adjuster body canthus be functionally operable after the imparting of the wear resistantsurface. The wear resistant surface layer can have a depth of less thanforty microns in some embodiments of the present disclosure. The wearresistant surface layer can have a depth of less than thirty microns insome embodiments of the present disclosure. The wear resistant surfacelayer can have a depth of less than twenty microns in some embodimentsof the present disclosure. The wear resistant surface layer can have adepth of between ten and twenty microns in some embodiments of thepresent disclosure. The wear resistant surface layer can have a depth ofbetween one and ten microns in some embodiments of the presentdisclosure.

At 110, the lash adjuster body can be subjected to cleaning and/orpolishing. Cleaning and polishing could be carried out concurrently orsequentially. Any mechanical methods can be applied to re-establish thesurface finish after a wear resistant surface layer is imparted. Aplurality of lash adjuster bodies can be cleaned and polished at onetime.

At 112, the lash adjuster body can be sized and sorted. The methoddiscussed above can produce more repeatable lash adjuster bodies therebyreducing categories for size and sort operations. Explained further,because (i) the conventional heat treating step that can alter thegeometry of the lash adjuster body and (ii) the subsequent machining(such as grinding) step that can further alter the geometry of the lashadjuster body are both eliminated, together less opportunities for theshape of the lash adjuster body to be distorted are presented. Thegeometries of the lash adjuster bodies are therefore more consistent.Inventory can be reduced. Capital cost can also be significantly reducedfor processing the components.

Referring again to FIG. 2, a lash adjuster assembly constructed inaccordance to one example of the present disclosure is shown andgenerally identified at reference number 10. The lash adjuster assembly10 is of the Type 2 valve train variety. It will be appreciated,however, that the teachings discussed herein with regard to the lashadjuster assembly 10 can be used in any configuration of lash adjusterand is not limited to the configuration shown in FIG. 2. The lashadjuster assembly 10 can generally include a lash adjuster body 20 and aleak down and ball plunger combination 22. The leak down and ballplunger combination 22 can include a ball plunger 23 and a leak downplunger 25. The discussion above that focused on a method of forming thelash adjuster body 20 may also be applicable to other components of thelash adjuster assembly 10 including, but not limited to, the ballplunger 23 and/or the leak down plunger 25 of the leak down and ballplunger combination 22.

The lash adjuster body 20 can generally extend along a longitudinal bodyaxis 30 and includes the outer cylindrical surface 32 and the innercylindrical surface 33. The inner cylindrical surface 33 can define theblind bore 40. A fluid aperture 42 can be defined through the lashadjuster body 20.

The lash adjuster body 20 can be assembled with the remaining componentsof a lash adjuster assembly 10. The components can then be provided intoa final lash adjuster assembly. Referring again to FIG. 2, the leak downplunger 25 and the ball plunger 23 can be inserted in the lash adjusterbody 20 at 114. As shown in FIG. 2, the leak down plunger 25 can bereceived in the inner cylindrical surface 33 of the lash adjuster body20. All or the majority of the inner cylindrical surface 33 can bepreserved in an as-formed condition and the leak down plunger 25 can beslidably engaged with the majority of the inner cylindrical surface 33during insertion. After assembly and in operation, the leak down plunger25 can be slidably engaged with the leak down portion 34 of the innercylindrical surface 33. In the exemplary lash adjuster body 20, themajority of the outer cylindrical surface 32 can also be preserved in anas-formed condition. The exemplary process can end at 116 in FIG. 1.

Referring again to FIG. 2, the leak down plunger 25 can be configuredfor reciprocal movement relative to the lash adjuster body 20 along thelongitudinal body axis 30. This movement can be sliding movement of theoutside surface of the leak down plunger 25 against the leak downportion 34 of the inner cylindrical surface 33. A plunger spring 50 canbe disposed within the blind bore 40 underneath the leak down plunger 25and be configured to bias the leak down plunger 25 in an upwarddirection (as viewed in FIG. 2) relative to the lash adjuster body 20.The plunger spring 50 can act at all times to elevate the leak downplunger 25 to maintain its engagement with the hemispherical concavesurface (not shown) of a rocker arm (not shown). In the example shown, aretaining member 60 is provided adjacent an upper portion of the lashadjuster body 20. The retaining member 60 limits upward movement of theleak down plunger 25 relative to the lash adjuster body 20 and retainsthe leak down plunger 25 within the lash adjuster body 20.

The lash adjuster assembly 10 includes a check valve assembly 70positioned between the plunger spring 50 and the leak down plunger 25 ofthe leak down and ball plunger combination 22. The check valve assembly70 functions to either permit fluid communication or block fluidcommunication between a low-pressure fluid chamber 76 and ahigh-pressure fluid chamber 78 in response to pressure differentialbetween the two fluid chambers 76 and 78. The check valve assembly 70can include a retainer 80 that is in engagement with the leak downplunger 25 of the leak down and ball plunger combination 22, a checkball 90, and a check ball spring 96 that is disposed between the leakdown plunger 25 and the check ball 90. The check ball spring 96 can beconfigured to bias the check ball 90 in a downward direction (as viewedin FIG. 2). The check valve assembly 70 can be referred to by thoseskilled in the art as “normally open.”

With reference now to FIG. 3, a lash adjuster assembly constructed inaccordance with another example of the present disclosure is shown andgenerally identified at reference number 10 a. The lash adjusterassembly 10 a can extend along an axis 30 a and generally include a lashadjuster body 20 a and a leak down and ball plunger combination 22 a. Anaperture 42 a can be defined in the lash adjuster body 20 a. The lashadjuster assembly 10 a can comprise similar components as describedabove, but be configured as a normally closed lash adjuster. The lashadjuster body 20 a can have an outer cylindrical surface 32 a and aninner cylindrical surface 33 a. The inner cylindrical surface 33 a caninclude a leak down portion 34 a, a blind bore 40 a, and a plunger shelf41 a. The lash adjuster body 20 a can be formed using the techniquesdescribed above. Specifically, the lash adjuster body 20 a can beconstructed using the method described above that avoids a heattreatment step and alternatively incorporates a process that imparts awear resistant surface layer such as FNC, PVD, or CVD.

FIG. 4 discloses another embodiment of the present disclosure. A lashadjuster assembly constructed in accordance with another example of thepresent disclosure is shown and generally identified at reference number10 b. The lash adjuster assembly 10 b can extend along an axis 30 b andgenerally include a lash adjuster body 20 b and a leak down and ballplunger combination 22 b. The lash adjuster body 20 b can have an outercylindrical surface 32 b and an inner cylindrical surface 33 b. Theinner cylindrical surface 33 b can include a leak down portion 34 b, ablind bore 40 b, and a plunger shelf 41 b. The inner cylindrical surface33 b can further comprise a notch 43 b. The notch 43 b can besemi-obovate in cross-section and be positioned between the leak downportion 34 b and the plunger shelf 41 b. Notches of other shapes can beapplied in other embodiments of the present disclosure. An aperture 42 bcan be defined in the lash adjuster body 20 b. The lash adjusterassembly 10 b can comprise similar components as described above, but beconfigured as a normally closed lash adjuster. The lash adjuster body 20b can be formed using the techniques described above. Specifically, thelash adjuster body 20 b can be constructed using the method describedabove that avoids a heat treatment step and alternatively incorporates asubcritical temperature process that imparts a wear resistant surfacelayer such as FNC, PVD, or CVD.

The lash adjuster body 20 b can define an inner diameter relief or hookportion 98 b. The hook portion 98 b can be created in the lash adjusterbody 20 b after a wear resistant surface layer is imparted. The wearresistant surface layer on the inside and/or outside of the hook portion98 b can be removed prior to crimping of the hook portion 98 b toprevent fracture or breakage. The hook portion 98 b can be crimped ordeformed to provide retention of the leak down and ball plungercombination 22 b within the lash adjuster assembly 10 b and caneliminate the need for bottle-caps, wires and clips to retain the leakdown and ball plunger combination 22 b. Alternatively, the hook portion98 b of the body 20 b, that is used for retention of the leak down andball plunger combination 22 b, can be used with conventional heattreatment of the lash adjuster body. In such application, the case orhard outer layers can be removed before crimping to prevent cracking orfracturing.

FIG. 5 discloses another embodiment of the present disclosure, a variantof the embodiment shown in FIG. 4. A lash adjuster assembly constructedin accordance with another example of the present disclosure is shownand generally identified at reference number 10 c. The lash adjusterassembly 10 c can extend along an axis 30 c and generally include a lashadjuster body 20 c and a leak down and ball plunger combination 22 c.The lash adjuster body 20 c can have an outer cylindrical surface 32 cand an inner cylindrical surface 33 c. The inner cylindrical surface 33c can include a leak down portion 34 c, a blind bore 40 c, and a plungershelf 41 c. The inner cylindrical surface 33 c can further comprise anotch 43 c. The notch 43 c can be semi-obovate in cross-section and bepositioned between the leak down portion 34 c and the plunger shelf 41c. Notches of other shapes can be applied in other embodiments of thepresent disclosure. An aperture 42 c can be defined in the lash adjusterbody 20 c. The lash adjuster assembly 10 c can comprise similarcomponents as described above, but be configured as a normally closedlash adjuster. The lash adjuster body 20 c can be formed using thetechniques described above. Specifically, the lash adjuster body 20 ccan be constructed using the method described above that avoids a heattreatment step and alternatively incorporates a subcritical temperatureprocess that imparts a wear resistant surface layer such as FNC, PVD, orCVD. The lash adjuster body 20 c can define an inner diameter relief orhook portion 98 c. The hook portion 98 c can be created in the lashadjuster body 20 c after a wear resistant surface layer is imparted.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A method of manufacturing a lash adjuster bodyfor use in a lash adjuster assembly, the method comprising: forming alash adjuster body to an as-formed condition including an outercylindrical surface and an inner cylindrical surface having a leak downportion and a blind bore; annealing the lash adjuster body to relievestresses arising during forming; subsequent to the annealing, impartinga wear resistant outermost surface layer to at least the leak downportion of the inner cylindrical surface with a sub-critical temperatureprocess using ferritic nitrocarburizing (FNC); and preserving the leakdown portion in the as-formed condition during imparting of the wearresistant surface layer.
 2. The method of claim 1 wherein forming isfurther defined as: forming a lash adjuster body with one of coldforming, stamping, drawing, metal injection molding, powdered metalsintering, and machining.
 3. The method of claim 1 wherein forming isfurther defined as: cold-forming the lash adjuster body to the as-formedcondition having functional geometry.
 4. The method of claim 3 whereinpreserving is further defined as: preserving a functional geometry ofthe leak down portion in the as-formed condition during imparting of thewear resistant surface layer.
 5. The method of claim 4 whereinpreserving is further defined as: preserving the functional geometry ofthe leak down portion in the as-formed condition after imparting of thewear resistant surface layer.
 6. The method of claim 1 furthercomprising: maintaining a hardness of the lash adjuster body below thewear resistant surface layer after forming and during imparting.
 7. Themethod of claim 1 wherein preserving further comprises: preserving theleak down portion of the inner cylindrical surface in the as-formedcondition after imparting of the wear resistant surface layer.
 8. Themethod of claim 1 wherein preserving further comprises: preserving amajority of the inner cylindrical surface in the as-formed conditionafter imparting of the wear resistant surface layer.
 9. The method ofclaim 1 wherein preserving further comprises: preserving a majority ofthe outer cylindrical surface in the as-formed condition after impartingof the wear resistant surface layer.
 10. The method of claim 1 whereinpreserving further comprises: preserving a majority of both of the outercylindrical surface and the inner cylindrical surface in the as-formedcondition after imparting of the wear resistant surface layer.
 11. Themethod of claim 1 further comprising: cleaning the lash adjuster bodyafter imparting; and polishing the lash adjuster body after imparting.12. The method of claim 1, further comprising: subsequent to impartingthe wear resistant surface layer, removing the wear resistant surfacelayer at a select portion of the lash adjuster body; and crimping theselect portion of the lash adjuster body to create a hook portionconfigured to retain a leak down and ball plunger of the lash adjusterassembly.
 13. A lash adjuster body for use in a lash adjuster assembly,the lash adjuster body comprising: an outer cylindrical surface; and aninner cylindrical surface having a leak down portion and a blind bore,wherein at least the leak down portion of the inner cylindrical surfaceincludes a wear resistant outermost surface layer imparted with asub-critical temperature process using ferritic nitrocarburizing (FNC)subsequent to annealing to relieve stresses and the leak down portion ispreserved in an as-formed condition existing prior to the imparting ofthe wear resistant surface layer.
 14. The lash adjuster body of claim 13wherein the inner cylindrical surface further comprises a plunger shelfand a notch positioned between the leak down portion and the plungershelf.
 15. The lash adjuster body of claim 13, further comprising: ahook portion formed on an area of the lash adjuster body without thewear resistant surface layer, the hook portion configured to retain aleak down and ball plunger of the lash adjuster assembly.
 16. A lashadjuster assembly comprising: a lash adjuster body having an outercylindrical surface, an inner cylindrical surface with a leak downportion and a blind bore, wherein at least the leak down portion of theinner cylindrical surface includes a wear resistant outermost surfacelayer imparted with a sub-critical temperature process using ferriticnitrocarburizing (FNC) subsequent to annealing to relieve stresses andthe leak down portion is preserved in an as-formed condition existingprior to the imparting of the wear resistant surface layer; and a leakdown plunger slidably received in the inner cylindrical surface againstthe leak down portion.
 17. The lash adjuster assembly of claim 16wherein a majority of the outer cylindrical surface and a majority ofthe inner cylindrical surface include the wear resistant surface layerand the majorities of the outer and inner cylindrical surfaces arepreserved in the as-formed condition existing prior to the imparting ofthe wear resistant surface layer.
 18. The lash adjuster assembly ofclaim 16 wherein a majority of the inner cylindrical surface includesthe wear resistant surface layer and a functional geometry of themajority of the inner cylindrical surface is maintained in the as-formedcondition existing prior to the imparting of the wear resistant surfacelayer.
 19. The lash adjuster body of claim 16 wherein the wear resistantsurface layer is further defined as having a depth of less than fortymicrons.
 20. The lash adjuster assembly of claim 16, further comprising:a hook portion formed on an area of the lash adjuster body without thewear resistant surface layer, the hook portion configured to retain theleak down and ball plunger.